System and method for converting chemical energy into electrical energy using nano-engineered porous network materials

ABSTRACT

An energy conversion device for conversion of chemical energy into electricity. The energy conversion device has a first and second electrode. A substrate is present that has a porous semiconductor or dielectric layer placed thereover. The porous semiconductor or dielectric layer can be a nano-engineered structure. A porous catalyst material is placed on at least a portion of the porous semiconductor or dielectric layer such that at least some of the porous catalyst material enters the nano-engineered structure of the porous semiconductor or dielectric layer, thereby forming an intertwining region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/130,386, filed Apr. 15, 2016, now U.S. Pat. No. 10/573,913, which isa continuation of U.S. patent application Ser. No. 13/945,864 filed Jul.18, 2013. Priority to these patent applications is expressly claimed,and the disclosure thereof is hereby incorporated herein by reference inits entirety. This application claims the benefit of ProvisionalApplication Nos. 61/676,285 filed Jul. 26, 2012, 61/712,712 filed Oct.11, 2012, 61/716,889 filed Oct. 22, 2012, and 61/724,764 filed Nov. 9,2012. Priority to these provisional applications is expressly claimed,and the disclosures of the provisional applications are herebyincorporated herein by reference in their entirety.

FIELD

This patent document relates generally to energy conversion systems andmore particularly relates to a method and system for converting chemicalenergy into electrical power using solid-state electric generators usingplanar or three dimensional surfaces that comprise porous materialnetworks such as a nano-wire arrays or nano-engineered structures, ornano-particles, or colloidal paste.

BACKGROUND

The use of solid state electric generators to convert chemical energyinto electricity has recently been demonstrated, as explained, forexample, in U.S. Pat. Nos. 6,268,560, 6,649,823, 7,371,962, and7,663,053. U.S. Pat. Nos. 6,268,560, 6,649,823, 7,371,962, and 7,663,053are hereby incorporated herein by reference in their entirety. Suchenergy conversion devices efficiently convert chemical energy toelectricity. For example, FIG. 1 herein illustrates a solid stateelectric generator along with graphs showing characteristics of such adevice. As shown in cross section in FIG. 1 -A herein, a charge carrier,usually an electron e⁻, is energized on or near a conducting surface 10Aby an energizer 12A. The charge carrier is energized, for example, bychemical reactions. In each case the charge carrier is injected into asemiconductor conduction band. For example, the charge carrierballistically moves from a conductor 10A into a semiconductor ordielectric 11A. The conductor 10A is so thin that the electroneffectively travels through it ballistically, without losing energy orcolliding with another electron or atom. Since an energy offset existsbetween the semiconductor conduction band and the Fermi level of thecatalyst, the result is a voltage 14A across positive terminal 17A andnegative terminal 16A. In FIG. 1 -A, the dielectric junction 15A is asemiconductor junction specifically chosen to create an electricalpotential voltage barrier which tends to impede the electron ballisticmotion, shown as 11B in FIG. 1 -B. FIG. 1 -B shows the electricalpotential in the device as a function of distance along the device atzero bias.

The potential voltage barrier can be formed in any one of many ways, forexample, a Schottky barrier as shown in FIG. 1 -C, a p-n junction inFIG. 1 -D, or a conductor-dielectric-conductor junction, FIG. 1 -E. Thedielectric is electrically conductive. A forward biased diode providesone of the simplest methods to implement this energy converting device.FIG. 1 -C depicts a forward biased Schottky diode whose positiveterminal is a conductor/metal.

SUMMARY

The present patent document describes various embodiments having novelthree dimensional device structures that can be on a planartwo-dimensional substrate or on a three-dimensional substrate. Thevarious embodiments improve on earlier solid state electric generatorsby increasing amount of power (i.e., electricity) that can be producedper unit of two-dimensional area of a device. The novel devicestructures described herein have solid-state junctions. These devicestructures comprise porous semiconductor or dielectrics andnano-clusters of conductor and/or catalyst to form the solid-statejunctions. Even though there are voids in the composite system,different porous semiconductor/catalyst materials, as an example, can bean integrated system or the materials may be physically connected as anetwork. Nano-clusters are when materials form nano-sized clusters. Thesolid-state junctions can be, but are not limited to, Schottky diodes orp-n junctions. Also disclosed are methods/processes to fabricate thedisclosed device structures, specifically for converting chemical energydirectly into electrical potential to produce power.

An energy conversion device for conversion of chemical energy intoelectricity is disclosed. A first aspect of the energy conversion devicecomprises a first electrode connected to a substrate. A poroussemiconductor (or dielectric) layer is disposed over the substrate (withan optional non-porous semiconductor (or dielectric) layer beingin-between the substrate on the porous semiconductor (or dielectric)layer. A porous catalyst material is located on at least a portion ofthe porous semiconductor (or dielectric) layer. At least some of theporous catalyst material enters the nano-engineered structure of theporous semiconductor layer, which forms an intertwining region. A secondelectrode is present, and an electrical potential is formed between thefirst electrode and a second electrode during chemical reactions betweena fuel, the porous catalyst material, and the porous semiconductornetwork.

In another aspect disclosed herein, the substrate of the energyconversion device is patterned to create a three-dimensional surface,thereby providing increased surface area for chemical reactions.

In another aspect disclosed herein, the substrate of the energyconversion device is patterned such that nano-wires are formed.

In another aspect disclosed herein, the substrate of the energyconversion device is textured such that peaks and valleys are formed.

In another aspect disclosed herein, the energy conversion device has anon-porous semiconductor layer in between the substrate and the poroussemiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included as part of the presentspecification, illustrate various embodiments and together with thegeneral description given above and the detailed description of theembodiments given below serve to explain and teach the principlesdescribed herein.

FIG. 1 -A illustrates a solid-state electric generator.

FIG. 1 -B illustrates a graph of potential energy versus distance fromthe device's topmost surface and indicating the effect of a potentialbarrier in a solid-state junction.

FIG. 1 -C illustrates a graph of potential versus distance from thedevice's topmost surface in an exemplary solid-state electric generatorhaving a Schottky barrier.

FIG. 1 -D illustrates a graph of potential versus distance from thedevice's topmost surface in an exemplary solid-state electric generatorhaving a p-n junction potential barrier.

FIG. 1 -E illustrates a graph of potential versus distance from thedevice's topmost surface in an exemplary solid-state electric generatorhaving a conductor-dielectric-conductor potential barrier.

FIG. 2 illustrates the energy band diagram for a catalyst-semiconductorinterface

FIG. 3 illustrates the schematics of EMF generation mechanism

FIG. 4 illustrates a schematic cross-section of a portion of a nanowirematerial array with a catalyst network.

FIG. 5 a depicts a cross-sectional view of a three-dimensional porousnetwork which consists of a porous catalyst three-dimensional layer thatintertwines three-dimensionally with another porous semiconductor ordielectric three-dimensional layer on a planar two-dimensionalsubstrate. A non-porous interlayer can optionally be inserted betweenthe planar substrate and the porous three-dimensional layers/networksabove.

FIG. 5 b is a cross-sectional microscopic view of a three-dimensionalporous network which consists of a porous catalyst three-dimensionallayer that intertwines three-dimensionally with another poroussemiconductor or dielectric three-dimensional layer.

FIG. 5 c is a top microscopic image of an energy converter having athree-dimensional porous network which consists of a porous catalystthree-dimensional layer that intertwines three-dimensionally withanother porous semiconductor or dielectric three-dimensional layer.

FIG. 6 shows an energy converter having a multi-cell device structurewith multiple layers of three-dimensional porous catalyst andthree-dimensional porous semiconductor or dielectric networks on aplanar substrate. A non-porous interlayer can be inserted or not betweenthe planar two-dimensional substrate and the porous three-dimensionallayers/networks above.

FIG. 7 shows an exemplary energy converter having a patternedthree-dimensional network of porous catalyst and porous semiconductor ordielectric on a three-dimensional substrates, in which the internal andexternal surfaces are covered with a porous semiconductor or dielectriclayer/network that intertwines with a porous catalyst layer/networkthree-dimensionally. An optional non-porous layer can also be insertedbetween the three-dimensional substrates and the three-dimensionalcatalyzed porous semiconductor or dielectric layer/network.

FIG. 8 shows an exemplary energy converter having three-dimensionalporous substrate/supporting layer (partially or fully) network of porouscatalyst and porous semiconductor or dielectric on a three-dimensionalsubstrates, in which the internal and external surfaces are covered witha porous semiconductor or dielectric layer/network that intertwines witha porous catalyst layer/network three-dimensionally. An optionalnon-porous layer can also be inserted between the three-dimensionalsubstrates and the three-dimensional catalyzed porous semiconductor ordielectric layer/network.

FIG. 9 a shows an exemplary energy converter having a texturedthree-dimensional network of porous catalyst and porous semiconductor ordielectric on a three-dimensional substrates, in which the internal andexternal surfaces are covered with a porous semiconductor or dielectriclayer/network that intertwines with a porous catalyst layer/networkthree-dimensionally. An optional non-porous layer can also be insertedbetween the three-dimensional substrates and the three-dimensionalcatalyzed porous semiconductor or dielectric layer/network.

FIG. 9 b is a microscopic image of a cross section of an exemplarythree-dimensional energy converter on a three-dimensional texturedsubstrate as in FIG. 9 a.

FIG. 9 c is a microscopic image of a top view of an exemplarythree-dimensional energy converter on a three-dimensional texturedsubstrate as in FIG. 9 a.

The above and other preferred features described herein, includingvarious novel details of implementation and combination of elements,will now be more particularly described with reference to theaccompanying drawings and pointed out in the claims. It will beunderstood that the particular methods and apparatuses are shown by wayof illustration only and not as limitations of the claims. As will beunderstood by those skilled in the art, the principles and features ofthe teachings herein may be employed in various and numerous embodimentswithout departing from the scope of the claims.

DETAILED DESCRIPTION

A method and apparatus for converting chemical energy into electricityis described. Each of the features and teachings disclosed herein can beutilized separately or in conjunction with other features and teachings.Representative examples utilizing many of these additional features andteachings, both separately and in combination, are described in furtherdetail with reference to the attached drawings. This detaileddescription is merely intended to teach a person of skill in the artfurther details for practicing preferred aspects of the presentteachings and is not intended to limit the scope of the claims.Therefore, combinations of features disclosed in the following detaileddescription may not be necessary to practice the teachings in thebroadest sense, and are instead taught merely to describe particularlyrepresentative examples of the present teachings.

In the following description, for purposes of explanation only, specificnomenclature is set forth to provide a thorough understanding of thevarious embodiments described herein. However, it will be apparent toone skilled in the art that these specific details are not required topractice the concepts described herein.

Moreover, the various features of the representative examples and thedependent claims may be combined in ways that are not specifically andexplicitly enumerated in order to provide additional useful embodimentsof the present teachings. It is also expressly noted that all valueranges or indications of groups of entities disclose every possibleintermediate value or intermediate entity for the purpose of originaldisclosure, as well as for the purpose of restricting the claimedsubject matter. It is also expressly noted that the dimensions and theshapes of the components shown in the figures are designed to help tounderstand how the present teachings are practiced, but not intended tolimit the dimensions and the shapes shown in the examples.

Device structures and methods/processes described herein, for example,in FIGS. 4-9 , include but are not limited to: (a) nanowires,nanofibers, or nanotubes; (b) porous nano-engineered structures withinterconnecting walls and pores; and (c) porous nano-engineeredstructures with percolating networks. Fabrication methods/processesinclude but are not limited to direct film growth resulting in porousstructures or/and nano-engineered structures. Methods of fabricatingsuch devices include but are not limited to (i) stain oxidation andetching; (ii) dry and/or wet oxidation and etching; (iii)electrochemical oxidation and etching; (iv) anodization oxidation andetching; (v) micro-arc oxidation and etching; nano-particles ofsemiconductor(s), dielectric(s), metal(s), catalyst(s), metal salts insolvents, pastes, or colloids; and (vi) solgel processes. For certainsemiconductors and dielectrics, e.g., silicon, only etching is requiredfor all these fabrication methods/processes to introduce porosity andnano-engineered structures in the materials.

In certain embodiments, a chemical energy conversion device is describedthat utilizes porous semiconductor or dielectric and porous catalystintegrated one unit/network on a planar two-dimensional substrate or athree-dimensional substrate. A porous thin film of dielectric orsemiconductor, such as a titanium dioxide (TiO₂), which is sometimesreferred to as titanium oxide, semiconducting network, can be fabricatedby depositing a thin film of metallic titanium (Ti) on a non-porousplanar substrate such as silicon, or on a non-porous supporting layerdeposited on a planar substrate, such as a non-porous TiO₂ layer onsilicon. This deposited thin metallic Ti film can subsequently beoxidized to create TiO₂ and further modified to form nano-porous holesin its microstructure through (i) stain oxidation and etching, (ii) dryor wet oxidation and etching, (iii) electrochemical oxidation andetching, (iv) anodization oxidation and etching, or (v) microarcoxidation and etching. Chemical reagents involved in all these processesinclude but are not limited to hydrofluoric acid (HF), nitric acid(HNO₃), sulfuric acid (H₂SO₄), hydrogen peroxide (H₂O₂), or/and sodiumhydroxide (NaOH). An additional non-porous layer of material functioningas a barrier layer can also be inserted between the deposited metallicTi thin film and the planar substrate in order to further enhance deviceelectrical performance. In another example the substrate itself can be athree-dimensional structure such as but not limited to porous silicon,textured silicon surfaces, and patterned silicon wafers. Likewise anadditional non-porous thin layer of semiconductor or dielectric such asTiO₂ may be inserted between the metallic Ti layer and thethree-dimensional substrate described above.

Although the various embodiments disclosed herein are described as usingTiO₂, wherever TiO₂, is discussed, other materials such as thin films ofporous semiconductors and dielectrics with nano-engineered structurescan be used without departing from the teachings herein. Such otherthin-film porous materials include but are not limited to silicon;Al₂O₃; GaN; GaAs; Ge; silica; carbon; oxides of niobium, tantalum,zirconium, cerium, tin, and vanadium. These materials also apply to theunderneath planar and three-dimensional substrates or supporting layers.The same processing methods can also be used in device fabrications.

As will be discussed, catalysts and/or conductors are placed on theinternal and external surfaces of the porous semiconductor to create aplurality (and preferably, and large number) of solid state junctions.The catalysts and/or conductors that can be used to form the solid-statejunctions with the porous nano-engineered semiconductor or dielectricnetwork(s) can be noble metals such as but are not limited to Pt, Au, orPd. These conductors and/or catalysts can be deposited using a number ofmethods, including but not limited to using nanoparticles or/and metalsalts in solvents, pastes, or colloids; thin film deposition followed byannealing to nucleate the formation of nano-particles or a combinationof pastes/solvent/deposition methods; chemical vapor deposition (CVD);sputtering; evaporation; atomic layer deposition (ALD); or solgelprocesses.

Turning to FIG. 2 , a mechanism for energy conversion is described. FIG.2 depicts an energy band diagram 200 for a catalyst-nanowire interfacefor an energy conversion device. Fuel plus oxidizer 205 comes intocontact with the catalyst 210, which oxidizes upon contact. The oxidizedfuel 210 injects electrons 240 into the conduction band 220 of thesemiconductor 215. There, the electrons 240 encounter a Schottky-likepotential barrier 225 between the semiconductor 215 and the catalyst210, which may be a conductor, and may also be a top electrode layer(not shown) that embeds the catalyst. The electrons 240 are thendirected towards the bottom contact (not shown) by the built-in electricfield at the interface between the catalyst 210 and the semiconductor215. The electrons 240 travel in the external circuit (not shown),thereby transferring their energy to the load before returning to thecatalyst site via the top contact (also not shown). The electrons 240then complete the reaction by reducing the oxidized reactants producingthe final products. The output voltage of the circuit shown in FIG. 2will depend on the potential offset (barrier) between the Fermi level inthe catalyst and the conduction band of the semiconductor.

Alternatively, the semiconductor/catalyst surface may favor one of theoxidation or reduction reactions, effectively splitting the tworeactions. This can create an electro-chemical potential gradientbetween the catalyst site and the semiconductor surface, which caninduce an electro-motive force (EMF) in an external circuit and drive aload as shown in FIG. 3 . In other words, as schematically shown in FIG.3 , the oxidation-reduction (redox) reactions induce an electron'schemical potential difference between the catalyst sites and thesemiconductor sites, which in turn gives rise to an EMF (Δμ=V₂−V₁).

The various embodiments described herein are chemical energy conversiondevices that convert chemical energy to electricity. A limiting factorof prior devices using similar electron transport mechanisms as thosedescribed herein was the rate at which catalytic reactions could takeplace. Electricity generation of chemical energy converter devices likethose described herein is proportional to the reaction rate and fuelconversion, and the reaction rate and fuel conversion are proportionalto at least (i) the temperature at which the catalytic reactions takeplace, and (ii) the total surface areas of the catalyst. Increasing thesurface area, however, generally leads to devices that become largetwo-dimensionally, and thus increases the size of the device, which isundesirable. Likewise, temperatures can be increased to enhance reactionrate, but increasing temperature can also be undesirable. The variousembodiments described herein overcome these problems by increasing thesurface area of the chemical energy converter device withoutsignificantly increasing the two-dimensional area of such devices.

FIG. 4 illustrates an embodiment of a chemical energy converter device400. In particular, FIG. 4 illustrates a device having nanowires 415,which are formed on a substrate layer (not shown), where the substratelayer can comprise a porous thin film of dielectric or semiconductor,such as a titanium oxide (TiO₂). The substrate layer is formed on anelectrode 410, which can be made with a metal conductive material orhighly n-doped semiconductor material. Electrode 410 can be below thesubstrate layer or in-between the substrate and the nanowires 415.Nanowires 415 can comprise either a nano-engineered porous semiconductormaterial or a nano-engineered porous dielectric. Either way, nanowires415 form an electrically conductive array. Catalyst material 420 is onthe surface of the nanowire 415, although intervening materials arepossible as well. The catalyst material 420 can be platinum particles,where each platinum particle forms a Schottky diode junction with thesemiconductor material forming the nanowires 415. In use, fuel or energysource 430 such as hydrogen, or methanol or natural gas, and air, or amonopropellant energy source or fuel such as hydrogen peroxide comes incontact with the catalyst 420, which causes electrons from the catalyst420 to be injected into the semiconductor 405, which are then attractedto the electrode 410. This generates electricity. A second electrode 425is formed over the catalyst 420, which, in conjunction with the bottomelectrode 410 allow a circuit to be formed so that electrical currentwill flow and a voltage potential V_(out) is generated between theelectrodes.

Nanowires 415 provide several advantages that improve the overallefficiency. The first advantage is increased surface area, which isprovided by both the use of a porous substrate 405 and nanowires 415.Porous three-dimensional structures have a high surface to volume ratiowhen compared to non-porous two-dimensional planar layers. In addition,the nanowires 415 themselves have surface area, meaning that eachnanowire 415 provides significantly more surface area than the sametwo-dimensional area would have provided were no nanowire 415 present.The additional surface area provided by the porous substrate 405 and thenanowires will have the ability to have more catalyst material disposedthereon, especially when compared to energy conversion devices that aretwo-dimensional. This is because presence of catalyst nano-particles,nano-clusters, or nano-wires on such a porous substrate provides morereaction sites for chemical reactions leading to increased reactionrates at lower temperatures. Another advantage is that porous networkalso facilitates diffusion of reactants to catalysts located on theinternal surfaces of the nanowires and removal of reaction products awayfrom the catalysts.

In an embodiment, nanowires 415 are comprised of single crystal TiO₂nanowires, which enhance electron transport, can be synthesized invarious simple inexpensive methods, such as growth from an epitaxialseed layer from a titanium source e.g. in a hydrothermal process. Thebottom contact 410 is a conductive substrate with a conductive layerthat provides an epitaxial template for nanowire growth, e.g. FTO(fluorinated tin oxide) in the case of TiO₂ nanowires. The top contact425 has to electrically connect the porous network of the catalyst. Thecatalyst can be a paste or an electrolyte. Again, the conductor and orcatalysts can be deposited used nano-particle pastes, nano-particlesolvents, thin film depositions or any combinations thereof.

FIG. 5 a illustrates another embodiment of an energy converter devicecomprising a three-dimensional porous catalyst layer 505 intertwinedthree-dimensionally with porous semiconductor or dielectric layer 515 atan intertwining region 510, which in turn can be placed on a planarsubstrate 525. Layer 515 can be constructed with TiO₂ as discussedabove, and can take the form of a honeycomb-like structure being eithera nano-engineered structure having interconnecting walls defining pores,or nano-engineered structures with percolating networks. Either way, thehoneycomb-like structure allows catalyst nano-particles from thecatalyst layer to enter the spaces of the honeycomb structure and reston the surface of the semiconductor or dielectric layer 515. It is thishoneycomb structure that makes layer 515 porous in three dimensions.These nano-particles can, for example, be platinum. The honeycomb-likestructure of the semiconductor or dielectric layer 515 can be seen inthe photographs of FIGS. 5 b -5 c.

Likewise, the three-dimensional porous catalyst layer 505 can compriseporous networks, individual nano-clusters/particles, or a combination ofboth, and can be constructed from, for example, platinum. As with poroussemiconductor or dielectric layer 515, catalyst layer can take the formof a honeycomb-like structure. An exemplary three-dimensional porouslayer 505 can be seen in the photographs of FIGS. 5 b-5 c . A feature ofthe intertwining region 510 is its large internal surface area wherecatalysts can be distributed throughout to construct a three-dimensionalnetwork of catalyst-semiconductor junctions. An exemplary intertwiningregion 510 can be seen in the photographs of FIGS. 5 b -5 c.

Chemical energy converter 500 can optionally include a non-poroussemiconductor or dielectric layer 520 deposited through standarddeposition methods such as evaporation, chemical vapor deposition (CVD),sputtering, or atomic layer deposition (ALD), to provide a barrier layerbetween the substrate below and the porous materials above.

In the embodiment illustrated by FIG. 5 , a top electrode 530 can beformed on part or all of catalyst layer 505. Likewise, a bottomelectrode 535 can be formed underneath planar substrate 520. These twoelectrodes can be electrically connected to an external load to form acomplete circuit.

FIG. 6 shows yet another embodiment, where a plurality of chemicalenergy converter devices 500 as in FIG. 5(a) are arranged as n cells 602a-602 n and are thus stacked on top of each other. A chemical energyconverter 600 as shown in FIG. 6 is a multi-cell device structure withmultiple layers of porous catalyst 605 a-605 n and poroussemiconductor/dielectric networks 615 a-615 n that can be fabricated andintegrated vertically on a planar two-dimensional substrate. Inparticular, chemical energy converter 600 can have a bottom electrode635, which has a planar substrate 625 disposed thereon. A non-poroussemiconductor or dielectric layer 620 can, if desired, be placed on theplanar substrate 625. Use of such a layer 620 acts as a barrier layerbetween substrate below and the porous materials above. The first cell602 a of the chemical energy converter 600 comprises a porous layer 615a comprised of a semiconductor or dielectric material, which can beconstructed, for example, from TiO₂. The first cell 602 a also comprisesa three-dimensional porous catalyst layer 605 a that is placed thereonusing methods described above, and can comprise porous networks,individual nano-clusters/particles, or a combination of both. Catalystlayer 605 a can be constructed from, for example, platinum. At theinterface between layer 615 a and catalyst layer 605 a, the materialsintertwine three-dimensionally in a first intertwined region 610 a.

To increase the amount of energy generated, chemical energy converterdevice 600 has additional cells 602 b through 602 n stacked on top ofeach other. For example, a second cell 602 b comprised of second porouslayer 615 b and second catalyst layer 605 b are formed above the firstcell, with a three-dimensional intertwined region 612 a formed betweenthe first cell 602 a and second cell 602 b. Likewise a thirdthree-dimensional intertwined region 610 b is formed between the secondcatalyst layer 605 b and second porous semiconductor or dielectric layer615 b.

To further increase energy generation, n additional cells 602 n can beadded to chemical energy converter 600. Each of the additional cells iscomprised of n second catalyst layers 605 n and n porous semiconductoror dielectric layers 615 n, with a three-dimensional intertwined region610 n formed at every interface between catalyst layers 605 n and poroussemiconductor or dielectric layer 615 n. A three-dimensional intertwinedregion 612 a-612 m will be formed between each cell. Such multi-cellstructures significantly increase the total catalyst-semiconductorinterfacial area without including a larger device, thereby increasingfuel conversion via chemical reactions and corresponding electricaloutput.

Yet another embodiment illustrated in FIG. 7 , in which a chemicalenergy converter 700 has the integration of porous catalyst and poroussemiconductor described in FIG. 5 constructed on a three-dimensionalsurface. Such a three-dimensional surface has surface area larger than aplanar two-dimensional substrate, which results in increased fuelconversion and reaction rates, which in turn increases the amount ofelectricity generated. In particular, the embodiment described withreference to FIG. 7 has a bottom electrode 735. A three-dimensionalsubstrate 725 is fabricated thereon using, for example, a standardlithography patterning/etching process. In this embodiment substrate 725forms a patterned three-dimensional network micro-trenches 712. Ifdesired, a non-porous layer 720 can be placed over the patternedsubstrate 725, which acts as a barrier layer between the substrate belowand the porous materials above. As in the embodiment shown in FIG. 5 , aporous semiconductor/dielectric network 715 is placed over patternedsubstrate 725 (or non-porous layer 720, if present). A catalyst layer705 is placed over the porous semiconductor/dielectric network 715,which also enters the pores of the porous semiconductor/dielectricnetwork 715 to form an intertwining region 710. A second electrode 730is placed above a catalyst layer 705, and in combination with firstelectrode 735, allows a voltage to appear, and hence allows for the useof the electricity generated by the converter device 700.

FIG. 8 shows an embodiment of a chemical energy converter 800 comprisinga porous three-dimensional substrate/supporting layer 825 where internaland external surfaces are covered with the integration of a poroussemiconductor or dielectric layer 815 and a porous catalyst 805 similarto that described in FIG. 5 . In particular, chemical energy converterdevice 800 has a bottom electrode 835, upon which a poroussubstrate/supporting layer 825 is placed thereon.

A second electrode 830 is placed above layer 825, and in combinationwith first electrode 835, allows a voltage to appear, and hence allowsfor the use of the electricity generated by the converter device 800.

Three-dimensional porous substrate is typically amorphous, which, uponannealing can crystallize. Nano-engineered structures typically consistof interconnected walls and wires forming a highly porous structure. Thesize of the pores, the thickness of the porous layer, among otherphysical and electrical properties, can be tuned by the processingparameters.

Another method to create a nano-engineered porous network or layer ofsemiconductor or dielectric, for example TiO₂, as a support to thecatalyst above it, is to utilize a paste of TiO₂ nano-particles to formthin films of porous layers/networks.

FIG. 9 a shows an embodiment having a three-dimensional texturedsubstrate/supporting layer 925 where the surface is covered with theintegration of porous semiconductor or dielectric material layer 915 andporous catalyst 905 like the embodiment described in FIG. 5 . Inparticular, the chemical energy converter 900 illustrated in FIG. 9 hasa bottom electrode 935. Placed thereon is a three-dimensional texturedsubstrate 925, which for example can be created by etching a siliconwafer.

Textured substrate 925 forms peaks and valleys, thereby creating athree-dimensional reaction area. This three-dimensional reaction areaincreases the surface area available for chemical reactions, whichincreases the number of reactive sites that can take place during aparticular amount of time for a given device size, thereby increasingthe electrical generation capability of the energy converter 900. Ifdesired, a non-porous layer 920 can be placed over the texturedsubstrate 905. As above, the non-porous layer 920 provides a barrierlayer to separate the substrate below and the porous materials above. Aporous or semiconductor or dielectric layer 915 is placed over thetextured substrate 925 (or non-porous layer, if present).

A catalyst layer 905 is placed over the porous semiconductor/dielectricnetwork 915, which also enters the pores of the poroussemiconductor/dielectric network 915 to form an intertwining region 910.A second electrode 930 is placed above a catalyst layer 905, and incombination with first electrode 935, allows a voltage to appear, andhence allows for the use of the electricity generated by the converterdevice 900.

As in the other embodiments described herein, the use of a texturedsubstrate 905 results in an increased surface area for catalysis, whichresults in greater electricity generation than an energy converterhaving a planar two-dimensional substrate.

FIG. 9 b is a photograph depicting an energy converter as in FIG. 9 ahaving a textured substrate. The photograph shows substrate 925 having asemiconductor or dielectric layer 915 formed thereon. Catalyst layer 905in the form of nano-particles is over the dielectric/semiconductor layer915, and nano-particles enter the pores of layer 915 to form anintertwining region. FIG. 9 c shows a planar view, where one can see thetexture of the dielectric/semiconductor layer 915.

Device structures, and methods/processes to fabricate them, usingnanowire arrays, nano-engineered structures, to form porous networkscomprising solid-state junctions specifically to convert chemical intoelectrical energy are described herein. The device structures can befabricated on a two-dimensional planar substrate or on athree-dimensional substrate. An exemplary method comprises fabricatingone or more solid-state electric generators. The solid-state electricgenerators include one or more chosen from the group including achemically energized solid-state electric generator. A solid stateelectric generator energizes charge carriers in a first material forminga junction with a second material. The second material has a finiteenergy gap with a conduction band that has an offset with the Fermilevel of the first material.

The present methods, devices and systems improve the energy conversionefficiency of junctions used in solid-state devices to generateelectricity. An energy source injects charge carriers, e.g. electrons,on one side of a junction. When a net excess of charge carriers isinjected from one side of a junction to the other, it will be forced totravel in the external circuit by the electric field. The result is theconversion of chemical energy into the useful form of an electricalenergy. An element of the embodiments is that the efficiency of thisprocess is improved when the charge transport or mobility is improved inthe semiconducting material.

An alternative mechanism for generating power is creating anelectrochemical potential difference between the nanowire network ornano-engineered porous networks/layers and the catalyst which can act asan electromotive force (EMF). The semiconductor/catalyst surface mayfavor one of the oxidation or reduction reactions, effectively splittingthe two reactions. This can create an electro-chemical potentialgradient between the catalyst site and the semiconductor surface whichcan induce an electro-motive force (EMF) in an external circuit anddrive a load.

One embodiment includes nanowire array or nano-engineered porousnetworks/layers made from dielectric or semiconductor including but notlimited to, for example, rutile TiO2, anatase TiO2, poly-crystallineTiO₂ porous TiO2, ZrO2, SrTiO₃, BaTiO3, Sr_x-Ba_y-TiO_z, LiNiO, silicon,SiC; GaN; GaAs; Ge; silica; carbon; oxides of niobium, tantalum,zirconium, cerium, tin, vanadium, and LaSrVO₃, and certain organicsemiconductors, such as PTCDA, or3,4,9,10-perylenetetracarboxylicacid-dianhydride. The subscripts x, yand z denote concentrations, per usual conventions. One advantage ofSrTiO₃ is that Schottky barriers on it may be unpinned, providing arelatively larger barrier compared to that of TiO₂.

Fuels, Oxidizers, Autocatalysts, Stimulators

The various chemical energy converter devices described herein usestorable reactants including oxidizers, autocatalytic reactionaccelerators, decelerators, and monopropellants. The liquid phase, suchas liquid hydrogen peroxide H₂O₂ at standard pressure and temperature,are convenient because their heat of vaporization is used as coolant andthe liquid is conveniently storable. Monopropellants such as H₂O₂ andmonomethylhydrazine (MMH) are similarly convenient and energize theactive surface of converters. Autocatalytic accelerators includemonopropellants such as H₂O₂.

One embodiment uses reactions and reactants to energize theseexcitations. The reactions, reactants and additives include at leastmonopropellants, high energy fuels with oxidizers, hypergolic mixtures,and additives and combinations of reactants known to produceautocatalytic specie, reactants chosen to accelerate reactions or tocontrol reactions, and combinations thereof. The reactants and/oradditives include but are not limited to the following reactants:

Energetic Fuels More Storable than Ammonia:

-   -   amine substituted ammonias    -   Di-Methyl-Amine (CH₃)₂NH    -   Tri-Methyl-Amine (CH₃)₃N    -   Mono-Ethyl-Amine (C2H5)NH2    -   Di-Ethyl-Amine (C₂H₅)₂NH)        Other Classes More Easily Storable:    -   Methanol, CH₃OH    -   Ethanol, EtOH CH3CH2OH    -   Formic Acid, HCOOH    -   diesel fuels    -   gasoline    -   alcohols    -   slurries including solid fuels    -   Carbon Suboxide, C₃O₂, CO═C═CO,    -   Formaldehyde HCHO,    -   Paraformaldehyde,=better HCHO)_(n), sublimeable to Formaldehyde        gas. (Potentially a cell coolant at the same time).        Less Storable Fuels:    -   Carbon Monoxide    -   Hydrogen    -   Ammonia NH3        Energetic Fuels Containing Nitrogen:    -   Nitromethane, CH₃NO₂    -   Nitromethane “cut” with Methanol=model airplane “glow plug”        engine fuel        High Energy Fuels with Wide Fuel/Air Ratio:    -   Epoxy-Ethane, =Oxirane or Ethylene-Oxide CH2-CH2 O    -   1,three-Epoxy-Propane=Oxetane and        Tri-Methylene-Oxide=1,three-Methylene-Oxide CH₂—(CH₂)—CH₂ O    -   Epoxy-Propane CH2-(CH2)-CH2 O    -   Acetylene, C₂H₂    -   Diacetylene=1,three-Butadiyne    -   1,three-Butadiene CH₂═CH—CH═CH₂,        Less Exotic High Energy Fuels:    -   Di-Ethyl-Ether or surgical ether    -   Acetone=Di-Methyl-Ketone        Less Exotic, Volatile Fuels:    -   Cyclo-Propane    -   Cyclo-Butane    -   Hydrocarbons such as methane, propane, butane, pentane, etc.        Other Storable Fuels:    -   Methyl Formate HCOO—C₂H₅    -   Formamide HCO—NH₂    -   N, N, -Di-Methyl-Formamide HCO—N—(CH₃)₂    -   Ethylene-Diamine H₂N—CH₂—CH₂—NH₂    -   Ethylene-Glycol    -   1,4-Dioxane=bimolecular cyclic ether of Ethylene-Glycol    -   Paraldehyde (CH₃CHO)₃ cyclic trimer of Acetaldehyde        Powerful Oxidizer:    -   Tetra-Nitro-Methane, C(NO₂)₄ . . . does not spontaneously        decompose . . . just pass the two separate vapors over the        reaction surface of the cell in the gas phase    -   Hydrogen Peroxide H2O2        Low Initiation Energy Mixtures:    -   Cyclo-Propane with Oxygen=surgical anesthetic, microjoules        initiator        Hypergolics:    -   UDMH=Unsymmetrical DiMethyl Hydrazine=1,1-DiMethyl Hydrazine        (CH₃)₂NNH₂    -   UDMH is hypergolic usually with N₂O₄ and is a very potent        carcinogen    -   MMH MonoMethyl Hydrazine (CH₃)HNNH₂ hypergolic with any        oxidizers, e.g. N₂O₄        Corrosive Toxic Energetic Monopropellant:    -   Hydrazine=H₂NNH₂ decomposed easily with a catalyst (usually Pt        or Pd or Molybdenum Oxide    -   Hydrazine Hydrate

Although various embodiments have been described with respect tospecific examples and subsystems, it will be apparent to those ofordinary skill in the art that the concepts disclosed herein are notlimited to these specific examples or subsystems but extends to otherembodiments as well. Included within the scope of these concepts are allof these other embodiments as specified in the claims that follow.

We claim:
 1. An energy conversion device for conversion of chemicalenergy into electricity, comprising: a first electrode; a substrateconnected to said first electrode; a three-dimensioned textured poroussemiconductor layer disposed over said substrate, said three-dimensionedtextured porous semiconductor layer having a nano-engineered structure;a porous catalyst material on at least a portion of saidthree-dimensioned textured porous semiconductor layer that contacts afuel and an oxidizer supplied to the energy conversion device, whereinat least some of the porous catalyst material enters the nano-engineeredstructure of said three-dimensioned textured porous semiconductor layerto form an intertwining region, the three-dimensioned textured poroussemiconductor layer forming solid-state junctions, wherein thesolid-state junctions are p-n junctions; and a second electrode, whereinelectrons from the porous catalyst material are injected into thethree-dimensioned textured porous semiconductor layer, and wherein anelectrical potential is formed between the first electrode and thesecond electrode during chemical reactions between the fuel and oxidizerin contact with the porous catalyst material.
 2. The energy conversiondevice of claim 1, wherein the substrate is patterned to create athree-dimensional surface, thereby providing increased surface area forchemical reactions.
 3. The energy conversion device of claim 2, whereinthe substrate is patterned such that nano-wires are formed.
 4. Theenergy conversion device of claim 2, wherein the substrate is texturedsuch that peaks and valleys are formed.
 5. The energy conversion deviceof claim 1, further comprising a non-porous semiconductor layer is inbetween the substrate and the three-dimensioned textured poroussemiconductor layer.
 6. The energy conversion device of claim 1, whereinthe porous catalyst layer is formed with nano-particles.
 7. The energyconversion device of claim 1, wherein the porous catalyst layer isformed with nano-clusters.
 8. The energy conversion device of claim 1,wherein the porous catalyst layer is formed with nano-wires.
 9. Theenergy conversion device of claim 1, wherein the three-dimensionedtextured porous semiconductor layer is formed with nano-particles. 10.The energy conversion device of claim 1, wherein the three-dimensionedtextured porous semiconductor layer is formed with nano-clusters. 11.The energy conversion device of claim 1, wherein the three-dimensionedtextured porous semiconductor layer is formed with nano-wires.
 12. Theenergy conversion device of claim 1, wherein the three-dimensionedtextured porous semiconductor layer is a porous nano-engineeredstructure with percolating networks.
 13. The energy conversion device ofclaim 1, wherein the three-dimensioned textured porous semiconductorlayer comprises a dielectric.
 14. The energy conversion device of claim13, wherein the dielectric is a porous nano-engineered structure withpercolating networks.
 15. The energy conversion device of claim 13,wherein the dielectric is formed with nano-particles.
 16. The energyconversion device of claim 13, wherein the dielectric is formed withnano-clusters.
 17. The energy conversion device of claim 13, wherein thedielectric is formed with the nano-wires.
 18. The energy conversiondevice of claim 1, where the three-dimensioned textured poroussemiconductor layer are chosen from a group including rutile TiO₂,anatase TiO₂, poly-crystalline TiO₂ porous TiO₂, ZrO₂, SrTiO₃, BaTiO₃,Sr_(x)Ba_(y)TiO_(z), LiNiO, silicon, SiC, GaN, GaAs, Ge, silica, carbon,oxides of niobium, tantalum, zirconium, cerium, tin, vanadium, LaSrVO3,perylenetetracarboxylic dianhydride (PTCDA), and3,4,9,10-perylenetetracarboxylic acid-dianhydride.
 19. The energyconversation device of claim 1, wherein the fuel and the oxidizercomprise a monopropellant.